On the snapshot below you can see the MessageBox shown when the user has clicked on a candle. The formatted text message takes detailed information from the underlying business object, which is accessible through the ChartItemClickEventArgs.DataPoint.DataItem.

The latest version of the Chart control includes an enhancement of the Selection mechanism. It allows the developer to programmatically select items in the control. The following code snippet demonstrates one such scenario:

Private Sub Button_Click(sender As Object, e As RoutedEventArgs)
For Each dataPoint1 As DataPoint In Chart1.DefaultView.ChartArea.DataSeries(0)
If dataPoint1.YValue = 154.0 Then
Chart1.DefaultView.ChartArea.SelectItem(dataPoint1)
End If
Next
End Sub

There are two main methods, which handle the selection. The first one is: Chart1.DefaultView.ChartArea.SelectItem - this method has a few overloads, but in general accepts a datapoint, or an index pointing to a specific datapoint in the chart series.
The Chart1.DefaultView.ChartArea.SelectItems method allows the selection of multiple datapoints, which are specified through the parameters.